Photocatalytic system: kinetics and mechanism of the photoreactions of octacyano complexes of molybdenum(IV) and tungsten(IV) with 1,2,3-indane-trione-hydrate

Abstract

The ligand field excitation of octacyano complexes of molybdenum(IV) and tungsten(IV) produces [M(CN) 7OH] 4− and a free cyanide ion. [M(CN) 7OH] 4− (M = Mo, W) reacts with 1,2,3-indane-trione-hydrate (ninhydrin) in 1:1 stoichiometry. The rate constants and quantum yields are at a maximum at pH 8.0. The rate of the reaction and the quantum yield increase with an increase in the ligand concentration and decrease with an increase in [M(CN) 8] 4− concentration. Quantum yields are higher for molybdenum than for tungsten owing to the shorter lifetime of the excited state species. This is because physical deactivation is expected to be more rapid in the heavier element due to enhanced spin—orbit coupling. Furthermore, molecular-orbital-induced splitting is larger in [W(CN) 8] 4− than in [Mo(CN) 8] 4− which results in a greater bond strength for tungsten.